package com.scau.hwadee.examination.utils;


import java.util.UUID;
import java.util.concurrent.atomic.AtomicLong;

/**
 * @author YHX
 * @date 2019/7/26  9:44
 * @description 产生id的三种方法
 */
public interface UniqueIDGeneratorUtils {

    /**
     * 产生一个唯一的ID值
     *
     * @return
     */
    String generatorId();

    /**
     * @author YHX
     * @date 2019/7/26  9:43
     * @description 1.内部类默认是public static
     * 2.产生32位不重复的id
     */
    class UUIDUniqueIDGeneratorUtils implements UniqueIDGeneratorUtils {
        public UUIDUniqueIDGeneratorUtils() {
        }

        @Override
        public synchronized String generatorId() {
            return UUID.randomUUID().toString().replace("-", "");
        }
    }

    /**
     * @author YHX
     * @date 2019/7/26  9:43
     * @description 这个方法就是用ipv4的地址来产生不同的id
     * 1.先获取电脑的ipv4地址，注意是ipv4地址，ipv6地址好像有点难搞，格式那些不好解决，ipv4就全部都是
     * 数字，好解决
     * 2.再随便加个长度和一个线程安全的自增数
     * 3.产生唯一的id值
     */
    class GlobalUniqueIDGeneratorUtils implements UniqueIDGeneratorUtils {
        private String seed;
        private final AtomicLong sequence = new AtomicLong(1L);
        private int length;

        public GlobalUniqueIDGeneratorUtils() {
            try {
                this.seed = LocalUtils.getLocalHost() + "-" + System.currentTimeMillis() + "-";
                this.length = this.seed.length() + "9223372036854775807".length();
            } catch (Exception var2) {
                throw new RuntimeException(var2);
            }
        }

        @Override
        public synchronized String generatorId() {
            StringBuilder sb = new StringBuilder(this.length);
            sb.append(this.seed);
            sb.append(this.sequence.getAndIncrement());
            String result = sb.toString();
            result = result.replace(':', '-');
            result = result.replace('_', '-');
            result = result.replace('.', '-');
            return result.replace("-", "");
        }

        public static void main(String[] args) {
            GlobalUniqueIDGeneratorUtils g = new GlobalUniqueIDGeneratorUtils();
            System.out.println(g.generatorId().length());
        }
    }

    /**
     * @author YHX
     * @date 2019/7/26  9:39
     * @description 雪花算法根据时间戳产生一个64位的不重复id，性能位于UUID和自增的主键id之间
     */
    class SnowFlake implements UniqueIDGeneratorUtils {
        /**
         * 起始的时间戳
         */
        private final static long START_STMP = 1480166465631L;
        /**
         * 每一部分占用的位数，就三个
         */
        private final static long SEQUENCE_BIT = 12;// 序列号占用的位数
        private final static long MACHINE_BIT = 5; // 机器标识占用的位数
        private final static long DATACENTER_BIT = 5;// 数据中心占用的位数
        /**
         * 每一部分最大值
         */
        private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
        private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
        private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);
        /**
         * 每一部分向左的位移
         */
        private final static long MACHINE_LEFT = SEQUENCE_BIT;
        private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
        private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
        /**
         * 数据中心
         */
        private long datacenterId;
        /**
         * 机器标识
         */
        private long machineId;
        /**
         * 序列号
         */
        private long sequence = 0L;
        /**
         * 上一次时间戳
         */
        private long lastStmp = -1L;

        public SnowFlake(long datacenterId, long machineId) {
            if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
                throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
            }
            if (machineId > MAX_MACHINE_NUM || machineId < 0) {
                throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
            }
            this.datacenterId = datacenterId;
            this.machineId = machineId;
        }

        /**
         * @return long
         * @author YHX
         * @date 2019/7/26  9:41
         * @params []
         * @description 产生下一个id
         */
        public synchronized long nextId() {
            long currStmp = getNewstmp();
            if (currStmp < lastStmp) {
                throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
            }

            if (currStmp == lastStmp) {
                /**
                 * if条件里表示当前调用和上一次调用落在了相同毫秒内，只能通过第三部分，序列号自增来判断为唯一，所以+1.
                 */
                sequence = (sequence + 1) & MAX_SEQUENCE;
                /**
                 * 同一毫秒的序列数已经达到最大，只能等待下一个毫秒
                 */
                if (sequence == 0L) {
                    currStmp = getNextMill();
                }
            } else {
                /**不同毫秒内，序列号置为0
                 * 执行到这个分支的前提是currTimestamp > lastTimestamp，
                 * 说明本次调用跟上次调用对比，已经不再同一个毫秒内了，
                 * 这个时候序号可以重新回置0了。
                 */
                sequence = 0L;
            }

            lastStmp = currStmp;
            /**
             * 就是用相对毫秒数、机器ID和自增序号拼接
             */
            return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                    | datacenterId << DATACENTER_LEFT      //数据中心部分
                    | machineId << MACHINE_LEFT            //机器标识部分
                    | sequence;                            //序列号部分
        }

        private long getNextMill() {
            long mill = getNewstmp();
            while (mill <= lastStmp) {
                mill = getNewstmp();
            }
            return mill;
        }

        private long getNewstmp() {
            return System.currentTimeMillis();
        }

        @Override
        public synchronized String generatorId() {
            return "" + nextId();
        }
    }

}
